Bioprocessing of glycerol MCQs With Answer

Introduction: Bioprocessing of glycerol MCQs With Answer is designed for M.Pharm students to deepen understanding of converting glycerol — especially crude glycerol from biodiesel production — into high-value chemicals via microbial and enzymatic routes. This compact quiz set focuses on biochemical pathways, microbial strains, fermentation strategies, downstream processing, analytical methods, and scale-up challenges relevant to pharmaceutical applications. Questions emphasize redox balance, enzyme cofactors, inhibition by impurities, and practical solutions used in industrial bioprocesses. Working through these MCQs will strengthen conceptual knowledge and prepare students for research or industry tasks involving glycerol valorization, process optimization, and regulatory considerations for pharmaceutical-grade products.

Q1. Which of the following is the primary industrial source of crude glycerol used for bioprocessing?

• Hydrolysis of carbohydrates in bioethanol plants
• Transesterification of triglycerides during biodiesel production
• Oligosaccharide fermentation in dairy waste
• Chemical synthesis from propylene oxide

Correct Answer: Transesterification of triglycerides during biodiesel production

Q2. What are the major impurities commonly found in crude glycerol that affect microbial fermentations?

• Cellulose, lignin and hemicellulose
• Methanol, salts (alkali), soaps and free fatty acids
• Monosaccharides and oligosaccharides
• Heavy metals like lead and mercury only

Correct Answer: Methanol, salts (alkali), soaps and free fatty acids

Q3. Which enzyme initiates the anaerobic conversion of glycerol to 3-hydroxypropionaldehyde (3-HPA) in many 1,3‑propanediol producing microbes?

• Glycerol kinase (EC 2.7.1.30)
• Glycerol dehydratase (coenzyme B12-dependent)
• Dihydroxyacetone kinase
• Glycerol oxidase

Correct Answer: Glycerol dehydratase (coenzyme B12-dependent)

Q4. Aerobic microbial oxidation of glycerol to dihydroxyacetone (DHA) commonly involves which enzyme?

• Glycerol dehydratase
• Glycerol dehydrogenase (NAD+-dependent)
• P450 monooxygenase
• Alcohol dehydrogenase specific for ethanol

Correct Answer: Glycerol dehydrogenase (NAD+-dependent)

Q5. Which statement correctly describes redox balance during anaerobic glycerol fermentation to 1,3‑propanediol?

• Formation of 1,3‑propanediol consumes ATP and produces NAD+
• Formation of 1,3‑propanediol consumes NADH and regenerates NAD+
• 1,3‑propanediol formation produces NADH and oxidizes NAD+
• Redox balance is independent of 1,3‑propanediol formation

Correct Answer: Formation of 1,3‑propanediol consumes NADH and regenerates NAD+

Q6. Which microorganism is classically used for industrial production of 1,3‑propanediol from glycerol?

• Saccharomyces cerevisiae
• Klebsiella pneumoniae
• Pseudomonas putida
• Bacillus subtilis

Correct Answer: Klebsiella pneumoniae

Q7. Why is residual methanol in crude glycerol a concern for glycerol fermentations?

• Methanol acts as a preferred carbon source and diverts flux away from desired products
• Methanol inhibits many microbial strains and can be toxic at moderate concentrations
• Methanol increases viscosity, preventing mixing
• Methanol is an essential cofactor for glycerol dehydratase

Correct Answer: Methanol inhibits many microbial strains and can be toxic at moderate concentrations

Q8. What is a common first processing step to remove methanol from crude glycerol before fermentation?

• Vacuum distillation to strip volatile methanol
• Activated carbon adsorption to remove methanol
• Ion-exchange resins specifically binding methanol
• Microfiltration to remove methanol

Correct Answer: Vacuum distillation to strip volatile methanol

Q9. In aerobic glycerol assimilation in many bacteria (e.g., E. coli), which enzyme phosphorylates glycerol to glycerol-3-phosphate?

• Glycerol dehydratase
• Glycerol kinase
• Dihydroxyacetone reductase
• Triacylglycerol lipase

Correct Answer: Glycerol kinase

Q10. Which cultivation condition usually favors 1,3‑propanediol formation from glycerol?

• Strictly aerobic fermentation with high dissolved oxygen
• Anaerobic or microaerobic conditions with low oxygen supply
• High shear continuous aeration
• High salt aerobic immobilized culture

Correct Answer: Anaerobic or microaerobic conditions with low oxygen supply

Q11. Which of the following is a major industrial challenge when using crude glycerol as feedstock at scale?

• Crude glycerol has a fixed composition identical across suppliers
• High and variable impurity profile (methanol, salts, soaps) affecting reproducibility
• It is too energy dense for microbial metabolism
• It readily forms stable emulsions that cannot be broken

Correct Answer: High and variable impurity profile (methanol, salts, soaps) affecting reproducibility

Q12. What is the theoretical stoichiometric molar conversion of glycerol to 1,3‑propanediol (PDO) under the simplified reaction glycerol → PDO?

• 2 mol glycerol → 1 mol PDO
• 1 mol glycerol → 1 mol PDO
• 3 mol glycerol → 2 mol PDO
• 1 mol glycerol → 0.5 mol PDO

Correct Answer: 1 mol glycerol → 1 mol PDO

Q13. Which cofactor is essential for the catalytic activity of the classical glycerol dehydratase?

• NADPH
• FAD
• Coenzyme B12 (adenosylcobalamin)
• Biotin

Correct Answer: Coenzyme B12 (adenosylcobalamin)

Q14. Why is it important to neutralize crude glycerol (adjust pH) prior to many fermentations?

• Crude glycerol is often highly acidic and neutralization produces methanol
• Crude glycerol is often alkaline due to residual alkali catalysts; pH adjustment prevents inhibition
• Neutralization increases glycerol chain length
• Adjusting pH precipitates glycerol for easier feeding

Correct Answer: Crude glycerol is often alkaline due to residual alkali catalysts; pH adjustment prevents inhibition

Q15. Which advanced approach can be used to manipulate cellular redox and improve yield of reduced glycerol products like 1,3‑PDO?

• Electrofermentation (applying an electrode potential to the culture)
• Adding high concentrations of oxygen to oxidize NADH
• Reducing temperature to near 0°C to slow metabolism
• Removing all salts to increase osmolarity

Correct Answer: Electrofermentation (applying an electrode potential to the culture)

Q16. Which analytical method is commonly used for simultaneous quantification of glycerol, 1,3‑PDO and organic acids in fermentation broth?

• HPLC with refractive index (RID) or UV detection
• Atomic absorption spectroscopy
• Nuclear magnetic resonance only (without chromatography)
• Light microscopy

Correct Answer: HPLC with refractive index (RID) or UV detection

Q17. What is a key advantage of using immobilized cells in continuous glycerol fermentations?

• Immobilized cells always eliminate mass transfer limitations
• They allow high cell densities and prolonged operational stability for continuous production
• Immobilized systems prevent any contamination risk
• They completely remove the need for downstream purification

Correct Answer: They allow high cell densities and prolonged operational stability for continuous production

Q18. Which genetic modification strategy is commonly employed to increase 1,3‑PDO production from glycerol?

• Overexpression of glycerol dehydratase and 1,3‑propanediol oxidoreductase and deletion of competing by‑product pathways
• Overexpression of lactate dehydrogenase to divert carbon to lactate
• Deleting glycerol uptake systems to slow substrate uptake
• Introducing cellulase genes to utilize glycerol better

Correct Answer: Overexpression of glycerol dehydratase and 1,3‑propanediol oxidoreductase and deletion of competing by‑product pathways

Q19. Typical mesophilic operating temperature range for fermentative glycerol conversion using organisms like Klebsiella sp. is:

• 5–15 °C
• 20–30 °C (commonly ~30 °C)
• 50–60 °C
• 80–90 °C

Correct Answer: 20–30 °C (commonly ~30 °C)

Q20. For pharmaceutical‑grade glycerol production from bioprocessed crude glycerol, which impurity is most critical to remove or limit according to regulatory expectations?

• Trace fungal spores
• Residual methanol
• High molecular weight polymers
• Inert dust particles

Correct Answer: Residual methanol

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